THE WATER CYCLE OF THE PETM: EVIDENCE IN HAND AND THE DATA WE WOULD LIKE TO HAVE

Meteoric water is an essential natural resource and a key component of the climate system that may be sensitive to anthropogenic global change. Changes in the water cycle represent a potential feedback mechanism on global climate change, and changes in the intensity and spatial distribution of hydrologic fluxes to and from the land surface may have profound impacts on the long-term habitability of regions of the continents where water balance is tenuous. Although very little observational evidence is available to document or test model predictions of the water cycle associated with greenhouse climates, a growing body of work supports the idea that substantial changes in the water cycle accompanied the transient, global, thermal maximum at the Paleocene-Eocene boundary (PETM). A pattern of increased environmental wetness, at least seasonally, across the northern mid-latitudes is supported by data on clay minerals abundances and terrestrial ecosystem-level carbon isotope discrimination, but significant gaps remain in our understanding of the generality, magnitude, and seasonality of these changes. Paleo-lacustrine systems, which integrate catchment-level information on terrestrial water balance, and estuarine or marginal marine systems, where changes in continental runoff may be recorded by paleosalinity proxies, represent hydrologically-sensitive depositional systems that may yield new information on the greenhouse water cycle of the PETM at the regional to continental scales.